1. Field of the Invention
This invention relates to liquid flow rate control devices, especially intravenous feeding control devices used in hospitals to control the flow rate of medical fluid.
2. Description of Prior Art
The feed rate of medical fluids during intravenous feeding is controlled by a device that automatically monitors and controls the flow rate in a feed tube. Such devices control the start time, feed rate, and stop time of the flow.
One method of flow control is to controllably squeeze the flexible feed tube with an electronically controlled clamp. However, it is very difficult to set the flow rate of a fluid precisely by clamping a flexible tube. The response of the flow to variations in constriction of the tube is extremely delicate. The clamp must be adjusted in steps of 0.001 mm, to provide adequate control. Medical fluid must be injected very slowly when a patient is in poor condition, and the flow must be controlled very precisely. For slow flow, the fluid tube must be flattened until it is barely open.
Prior apparatus for providing such delicate control is relatively complicated, large, and heavy. Prior devices are too heavy to hang on the medical tube without support, so attachment of the controller to a stand is required.
An example of a prior intravenous feeding control device having a wedge to squeeze a medical fluid tube for flow rate control is disclosed in the Patent Abstracts of Japan No. 1996-8317974.
The main objective of this invention is provision of a small, lightweight intravenous feeding control device capable of controlling the flow rate medical fluid very precisely. A further objective is an intravenous feeding control device that can be hung directly from a medical fluid feed tube without the need for attachment to a stand. Other objectives include simplicity of production, low expense, and high reliability.
The objectives are achieved in a liquid flow rate detector and controller having a microprocessor that senses the rate of drops falling in a monitoring balloon on a fluid tube. A light emitter/detector pair detects drops as they fall in the balloon, which are timed by the microprocessor. The device has first and second switches manufactured in a single small assembly made of thin laminates. Each switch comprises an electrode and a contact point, mutually facing across a gap in the layers. The lamina on at least one side of each switch is elastic. External force flexes the elastic layer, causing it to bend across the gap, causing the contact point to touch the electrode. A fluid tube is inserted in a narrow channel between the first switch and a movable wedge. A stepper motor under control of the microprocessor moves the wedge to press the fluid tube against the first switch until the contacts close. This indicates that the fluid tube is completely flattened and closed. The microprocessor then retracts the wedge a predetermined distance from the closed point and monitors the rate of drops falling in the drip balloon. The movement of the wedge is precisely controlled by the microprocessor to achieve a desired drop rate. The second switch senses the presence of a fluid tube in the narrow channel to allow initialization of the process.